1. Field of the Invention
The present invention relates to a radial tire manufacturing method, and particularly to a radial tire manufacturing method which allows reduction in radial force variation (RFV) of a radial tire.
2. Description of the Related Art
In a radial tire, conventionally, due to non-uniformity (hereinafter referred to as radial run-out or RRO) in a radial direction of a green tire, which is caused by formation of tire structural members, and vulcanization factors of a vulcanizer, radial direction force variation (RFV) is generated in a vulcanized tire.
The RFV of a radial tire greatly affects vehicle vibrations and the comfort of ride, and therefore, various attempts to reduce the RFV have been made.
Typically, as disclosed in Japanese Patent Application Publication (JP-B) No. 4-76295, a radial tire manufacturing method has been proposed in which an average waveform of force variation of a green tire, which is a molding factor, and an average waveform of force variation of a vulcanization mold, which is a vulcanization factor are offset with each other. However, in this method, a difference is made between the average waveform of force variations of green tires and each of force variation waveforms of green tires, and therefore, these factors cannot sufficiently be offset. Accordingly, the force variation could not sufficiently be reduced.
Further, there has been proposed, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 6-182903, a radial tire manufacturing method in which a waveform of radial run-out (RRO), that is, out of roundness, of a green tire and a waveform of a vulcanization factor are offset with each other. In this method, the molding factor is replaced by the RRO waveform of a green tire, but a rigidity factor which cannot be detected in the RRO waveform, or gauge variation caused by slippage of a cap and a layer member during vulcanization in a high-performance tire is not taken into consideration. Accordingly, the radial force variation (RFV), that is, variations of reaction force acting in a radial direction could not sufficiently be reduced.
The above-described rigidity factor and gauge variation are each a molding factor (fixed factor) determined based on a tire construction.
In view of the above-described facts, it is an object of the present invention to provide a radial tire manufacturing method in which force variation in a radial direction of each tire can be sufficiently reduced.
In accordance with a first aspect of the present invention, there is provided a radial tire manufacturing method comprising the steps of: (a) measuring an radial run-out (RRO) waveform of each green tire; (b) recording an average waveform component of radial force variation (RFV) of a molding factor in each molding machine for molding a green tire, and an average waveform component of RFV of a vulcanization factor in each vulcanizer for vulcanizing a green tire, in a computer, including the step of obtaining the average waveform component of RFV of the molding factor and of the vulcanization factor; (c) obtaining an RFV composite waveform including the sub-steps of: (1) converting an RRO waveform of each green tire into an RFV waveform component;
and (2) synthesizing respective average waveform components of RFV by the molding factor and by the vulcanization factor, with the RFV waveform component; (d) selecting a circumferential position on a green tire at which an amplitude of the RFV composite waveform becomes minimum, and a circumferential position in the vulcanization mold; and (e) vulcanizing the green tire including the sub-steps of: (1) positioning the circumferential position on the green tire to the circumferential position in the vulcanization mold; and (2) loading the green tire in the mold.
The radial tire manufacturing method according to the first aspect of the present invention will be described hereinafter.
In the radial tire manufacturing method according to the first aspect of the present invention, first, in the RRO waveform measuring step, an RRO waveform of a green tire to be vulcanized is measured by a laser displacement meter or the like, and inputted to a computer.
Further, in the average waveform recording step, an average waveform component of RFV by a molding factor is in advance acquired for each molding machine and is recorded in a computer, and an average waveform component of RFV by a vulcanization factor is in advance acquired for each vulcanizer and recorded in a computer.
In the waveform synthesizing step, an RFV waveform component obtained by converting the RRO waveform of a green tire is made to overlap with respective average waveform components of RFV by the molding factor and the vulcanization factor, and an RFV composite waveform is thereby obtained.
In the selection step, the circumferential position on the green tire at which an amplitude of the RFV composite waveform becomes minimum, and the circumferential position in the vulcanization mold are selected.
In the vulcanization step, based on the circumferential position on the green tire at which an amplitude of the RFV composite waveform becomes minimum, and the circumferential position in the vulcanization mold, which positions are selected in the selection step, the green tire is mounted and disposed in the vulcanization mold, and thereafter, vulcanized.
As a result, a radial tire of which radial direction force variation (RFV) is sufficiently reduced can be obtained.
In the radial tire manufacturing method according to the present invention, preferably, the step of recording an average waveform component of radial force variation (RFV) of a molding factor in each molding machine for molding a green tire, and an average waveform component of RFV of a vulcanization factor in each vulcanizer for vulcanizing a green tire, in a computer, wherein the step comprises the sub-steps of: (1) sampling at least two vulcanized tires; (2) offsetting the molding factor from a plurality of RFV waveforms of the vulcanized tires; and (3) obtaining an average waveform component of RFV by the vulcanization factor.
Next, a preferable method of manufacturing a radial tire according to the present invention will be described.
In the radial tire manufacturing method of the present invention, preferably, in the average waveform recording step, at least two vulcanized tires are used as samples, and by offsetting a molding factor from a plurality of RFV waveforms obtained from vulcanized tires, the average waveform component of RFV by a vulcanization factor is acquired.
The number of samples of vulcanized tires used to offset the above-described molding factor is at least two, but when a large number of samples is used, a high-accurate average waveform component of RFV by a vulcanization factor can be obtained.
In the radial tire manufacturing method according to the present invention, preferably, the step of recording an average waveform component of radial force variation (RFV) of a molding factor in each molding machine for molding a green tire, and an average waveform component of RFV of a vulcanization factor in each vulcanizer for vulcanizing a green tire, in a computer, wherein the step comprises the sub-steps of: (1) sampling at least two vulcanized tires; (2) offsetting the molding factor from a plurality of RFV waveforms of the vulcanized tires; and (3) obtaining an average waveform component of RFV by the molding factor.
Next, a preferable method of manufacturing a radial tire of the present invention will be described.
In the radial tire manufacturing method of the present invention, preferably, in the average waveform recording step, at least two vulcanized tires are used as samples, and by offsetting a vulcanization factor from a plurality of RFV waveforms obtained from vulcanized tires, the average waveform component of RFV by a molding factor is acquired.
The number of samples of vulcanized tires used to offset the above-described vulcanization factor is at least two, but when a large number of samples is used, a high-accurate average waveform component of RFV by a molding factor can be obtained.
In the radial tire manufacturing method according to the present invention, preferably, the step of recording an average waveform component of radial force variation (RFV) of a molding factor in each molding machine for molding a green tire, and an average waveform component of RFV of a vulcanization factor in each vulcanizer for vulcanizing a green tire, in a computer, wherein: if at least two vulcanization molds are provided in a vulcanizer, including the steps of: (1) obtaining an average waveform component of RFV by a vulcanization factor for each vulcanization mold; and (2) recording the average waveform component of RFV by a vulcanization factor in a computer.
Next, a preferable method of manufacturing a radial tire of the present invention will be described.
In the radial tire manufacturing method of the present invention, preferably, when the vulcanizer includes at least two vulcanization molds, in the average waveform recording step, an average waveform component of RFV by a vulcanization factor is acquired in each vulcanization mold and is record in a computer.
As a result, a green tire can be suitably vulcanized in each vulcanization mold.
In the radial tire manufacturing method of the present invention, more preferably, the selection step includes identifying the circumferential position on the green tire at which the RFV composite waveform has minimal amplitude and applying a bar code on the green tire for identifying this position.
Next, a more preferable method of manufacturing a radial tire according to the present invention will be described.
In the radial tire manufacturing method of the present invention, in the selection step, preferably, the bar code applied to the green tire identifies the selected circumferential position on the green tire.
In a conventional tire manufacturing step, in order to manufacture a tire having suitable uniformity, a green tire is mounted in a vulcanization mold so that, for example, a peak position of RRO of the green tire and a bottom position of RRO of the vulcanization mold coincide with each other.
When a bar code is applied to a green tire in a preferred embodiment of a method according to the present invention, it is not necessary to specifically indicate the peak position of RRO. The bar code is therefore advantageously used for identifying the selected the circumferential position on the green tire.
In the radial tire manufacturing method of the present invention, preferably, setting of the circumferential position on the green tire and the circumferential position in the vulcanization mold in the vulcanization step is effected on any one of a green tire stand and a loader.
Next, a still more preferable method of manufacturing a radial tire according to the present invention will be described.
In a conventional tire manufacturing step, a green tire is temporarily placed on a green tire stand on which the green tire can be rotatably supported, before being mounted and disposed in a vulcanization mold. The green tire placed on the green tire stand is conveyed by a loader to the vulcanization mold and is mounted at a predetermined position in the vulcanization mold.
The green tire stand supports rotatably the green tire placed thereon, and the loader is rotatable in a state of holding the green tire. Accordingly, setting of the circumferential position on the green tire and the circumferential position in the vulcanization mold can be directly conducted on the green tire stand or in the loader.